The Cancer Epidemiology and Prevention Research Center supports a broad program of studies investigating the etiology of various cancers with the ultimate objective being the development of knowledge that can be used for cancer prevention. The epidemiology of breast cancer has been a major component of the Center's program. The primary hypothesis being tested in the etiology of breast cancer is the relationship of a woman's estrogen metabolism during the first decade after menarche to her risk of breast cancer. The roles of exogenous hormones (oral contraceptives and Premarin) are being evaluated for their relationship to breast cancer, benign breast disease, cancer of the endometrium, and cancer of the corpus uteri. Hodgkin's disease is another major component of this program. The roles of environmental exposures and person-to-person transmission are being studied. Other studies include cancer of the pancreas, and gastric cancer.